The invention relates to a heating device for motor vehicles with a water-cooled internal combustion engine.
In a known heating device (German Patent Document DE 19 61 286 A1), a thermostatically activated switching element has three valves and a bypass between two inlets of the valve. A first valve is constructed as a non-return valve and is directly assigned to the outlet, connected to the auxiliary heating unit, of the switching element. A second valve which is controlled by the thermostat controls the connection between the first inlet, connected to the heat exchanger, and the outlet as well as the connection between a second inlet, connected to the water cooling circuit of the engine, and the outlet of the switching element. A third valve which is controlled by the thermostat is directly assigned to the second inlet of the switching element.
When the engine is deactivated (stationary mode) and the auxiliary heating unit is switched on, the third valve is closed and the second valve is opened and the heat exchanger is connected to the auxiliary heater. When a prescribed water temperature is reached, the thermostat opens the third valve and hot water flows via the heat exchanger on the one hand and via the cold engine on the other, and the engine is preheated. As the temperature rises further, the thermostat closes the second valve and blocks off the heat exchanger. The water which is heated by the auxiliary heating unit flows exclusively via the engine and brings it up to operating temperature. If the engine is started and if it supplies sufficient hot water via the cooling water circuit and if the auxiliary heating unit is switched off, hot water is pumped back to the engine via the heat exchanger, via the bypass and via the opened third valve by the water pump in the cooling circuit of the engine. Such a switching element with three valves, a thermostat and a bypass has a very complex structure and makes the heating device more expensive without substantially increasing its effectiveness.
In a known heating device of the type mentioned at the outset (German Patent Document DE 43 14 089 Cl), the thermostat which is arranged in the outflow chamber and is constructed as an element made of expanding material activates a main valve plate which is pressed in a sealing fashion under the force of a closing spring onto a flange ring which is arranged between the inflow chamber and outflow chamber. At a selectable set temperature of the heating water which flows from the auxiliary heating unit to the heat exchanger via the outflow chamber, the thermostat which is arranged in the outflow chamber lifts off the main valve plate from the flange ring and some of the heating water flows out of the outflow chamber via the inflow chamber into the cooling water circuit of the internal combustion engine so that the latter is preheated and reaches its operating temperature more quickly. The nonreturn valve which is also arranged between the inflow chamber and outflow chamber and has a blocking direction which points towards the inflow chamber is formed by a subsidiary valve plate which is pressed on to the main valve plate under the force of a compression spring and, at the same time, closes off the through-holes present in the main valve plate. The subsidiary valve plate lifts off from the main valve plate and thus clears the connection between the inflow chamber and outflow chamber if the pressure, produced by the circulation pump after the circulation pump in the cooling water circuit of the internal combustion engine is switched on, is high enough to overcome the pressing-on force of the compression spring. Thus, the heated-up cooling water which flows into the inflow chamber from the internal combustion engine returns to the internal combustion engine via the outflow chamber and the heat exchanger as well as through the auxiliary heating unit. If the temperature of the cooling water exceeds the set temperature of the thermostat, the latter also lifts off the main valve plate from the flange ring so that a greater flow orifice between the inflow chamber and outflow chamber is cleared. Such a switching element with two integrated valves is constructionally very complex, which results in substantially higher production costs of the switching element.
An object of the invention is to substantially simplify, and make less susceptible to faults, the switching element in a heating device of the type mentioned at the outset, and, at the same time, maintain the fundamental mode of operation of engine heating and stationary-mode heating.
This object is achieved according to the invention in a heating device for motor vehicles of the generic type discussed above by providing an arrangement wherein the inflow chamber and outflow chamber are connected to one another via at least one leakage hole, and wherein the thermostat is arranged in the inflow chamber and has an activation element which lifts off the valve element of the non-return valve from its valve seat above a prescribed temperature.
In the heating device according to the invention, apart from the thermostat the switching element only contains a single valve and constitutes a complete unit which is easy to produce, simple to mount and only has to be connected to the rest of the heating system at the three connectors. The switching valve which is constructed as a non-return valve with additional activation by the thermostat is robust and has little susceptibility of faults.